Seed meters of various designs have been used for some time to dispense seeds at a controlled rate into a seed furrow as the seed meter is advanced above and along the seed furrow. In a typical arrangement, a tractor is coupled to tow a tool bar to which are attached in a generally parallel, spaced apart relation a plurality of planting units with seed meter arrangement attached thereto. Each planting unit typically includes a seed hopper for containing and carrying a large quantity of seeds to be planted or a smaller container fed from a centralized bin or large hopper, a device for opening a furrow in the ground as the tractor drawn tool bar is advanced across the field over the ground, a seed meter coupled to the seed hopper for dispensing individual seeds into the furrow at a controlled rate, and a further device for moving soil at the sides of the furrow to close the furrow over the seeds.
During a planting operation, the tractor typically moves across the field at speeds of about 4 to about 8 miles per hour. The spacing between adjacent individual seeds in each furrow can be as little as 0.5 inches or less or as much as 10 inches or more depending upon the particular seed being planted. The seed metering mechanism therefore must be capable of dispensing seeds at various rates in the order of 15 to 130 seeds per second or greater as well as at rates which are considerably less.
Some seed metering systems used in planting operations of the type discussed above are of the mechanical type and include a vertical or horizontal seed plate or disc with mechanically actuated fingers or similarly operated mechanical devices for separating individual seeds from the seed disc and then dispensing them into the furrow. While some mechanical seed meters are satisfactory for certain applications, they typically suffer from a number of limitations including the limited speed at which they can accurately dispense seeds, an inability to handle different type seeds without making cumbersome and extensive part changes, and an inherent design complexity which may typically add to the cost, wear and maintenance problems of the mechanically operated seed dispensing systems.
Alternatively, a seed metering mechanism which utilizes an air pressure differential has been developed in an effort to overcome some of the problems of the mechanical seed meters. Air pressure differential seed meters, which are commonly known as air seed meters, are generally of two types: the first type being the positive pressure type and the second type relying upon negative pressure or vacuum.
In the positive pressure type air seed metering mechanism, air is blown into the seed chamber and onto the surface of a rotating or otherwise movable and opening member or disc in order to create an air pressure greater than atmospheric pressure in the chamber. This forces seeds from a seed mass onto the seed member or disc where they are retained for later release. The openings or holes in the rotating member or disc are open to atmosphere, such that the individual seeds are held by the blowing air until the seeds are dispensed by interrupting the flow of air to the seeds.
Vacuum seed metering systems typically include a rotatable disc mounted for rotation within a hollow interior of a generally cylindrical two-piece housing mounted at the bottom of a seed hopper. Seeds from the seed hopper flow into a seed chamber within the housing on a side of the seed disc having a plurality of through openings provided in a circumferential arrangement adjacent the periphery of the disc. As the seed disc rotates, the openings are arranged such that they pass through the seed chamber and the seeds are drawn to the openings and held therewithin as the seed disc rotates. In vacuum seed metering mechanisms, as the seed disc rotates, the seeds are held in relation to the seed disc by a vacuum source coupled to a separate chamber on the opposite side of the seed disc from the seeds in the seed chamber. Because the pressure differential at the seed disc comes from a vacuum source on a side of the disc opposite from the seed chamber, the problem of having to direct an air flow through the seed mass and onto the seed disc is eliminated.
As is conventional, the vacuum communicates with the openings in the seed disc which extend through the thickness of the seed disc. As the individual seeds are carried by the seed disc, they eventually reach a discharge area from whence the seeds are discharged from the seed disc for gravitational deposit into the furrow passing beneath the seed metering mechanism. This is accomplished by isolating the effects of the vacuum or pressure differentials acting on the seed disc in the discharge region or area of the seed metering mechanism.
In vacuum seed metering systems, it is necessary that the vacuum chamber within the housing of the seed metering mechanism be sealed against atmospheric air so that the vacuum acting on the seeds can be confined to a particular path of movement of the openings in the seed disc. This requires sealing of the region between the outer periphery of the disc and the inner radial distance defined by the innermost circular row of openings in the disc. Complicating this requirement is the fact that the seed metering disc rotates at a speed which can be substantial.
Each of the above described seed metering systems includes a first stationary metering member against which a second metering member having a plurality of seed engaging surfaces moves to carry individual seeds from the seed mass. For example, the vertical or horizontal seed plate of mechanical type seed metering systems typically rotates adjacent to the housing or other structure. In positive pressure types air seed metering systems, a drum having openings extending therethrough is typically rotated adjacent to a housing or other structure. With vacuum seed metering systems, a seed disc having openings extending therethrough is rotated adjacent to the housing or other structure. As a result, the bearing surfaces between the first and second metering members wear over time. This wear of the bearing surfaces accelerates when particles of dirt, seed treatment and other abrasive particles become captured between the first and second bearing surfaces. As the members move or rotate relative to one another, the particles abrade away at the bearing surfaces. As a result, this accelerated wear of the bearing surfaces requires that either the seed disc, the adjacent housing or both members be replaced more frequently.
Various attempts have been made to remove the abrasive materials and thereby prolong the life of the seed disc or abutting housing. One such attempt at removing abrasive materials has been the provision of a notch or cut-out in the small portion of the bearing surface of the adjacent housing. The notch defines a radially extending wall which scrapes material away from the opposing bearing surface. The notch is typically located at a bottom side of the housing such that material removed by the wall falls away from the housing under the force of gravity. Because the wall formed by the notch is radial, gravitational force is the only force applied to the abrasive material to remove the abrasive material from the seed disc. If the abrasive material is further mixed with grease or other sticky substances, the abrasive material will simply cling to the wall and will continue to abrade the rotating seed disc.
Another such attempt has been the provision of triangular depressions in the bearing surface of the cover. The triangular depressions typically have a wide base communicating with the vacuum chamber and narrow peak. One of the plurality of triangular depressions has a peak communicating with atmosphere.
These triangular depressions, alone, have been found to be ineffective at removing abrasive material. First, because the triangular depressions are formed at spaced locations in the bearing surface of the cover, which is stationary, the abrasive materials along substantial portions of the bearing surface of the cover are not removed. Consequently, these abrasive materials remain and continue to abrade both bearing surfaces of the seed disc and the cover. Second, the majority of the triangular depressions only communicate with the vacuum. As a result, such triangular depressions must rely solely upon scraping action to remove abrasive material. Because all the depressions are triangular in shape, removed abrasive material moves along the edge of the triangular depressions towards the peak of the triangular depression and away from the vacuum chamber. Thus, abrasive materials build up within the peak of the triangular depression and remain within the triangular depression to continue to abrade and wear the seed disc.
Thus, there is a continuing need for a seed metering system which effectively reduces abrasive materials between bearing surfaces of the metering members which move relative to one another to prolong the useful life of the metering members.